How prevent reload after post request?

Question

I am trying to make a post request to the server and do something with the response. Things seem to work on the server-side. The problem is that the page reloads upon completion of the response and I cannot do anything with the response.

The common suggestions are using button or preventDefault . These suggestions do not solve the problem: as you can see below, the input type is button (not submit ) and preventDefault() on the event does not work.

Does anyone have an idea about what I am missing?

 <form id="modelCodeForm">
    <label for="codehere"></label>
    <div id="modelAreaDiv">
      <textarea id="modelArea" cols="60" rows="20">
stuff
      </textarea>
      <br>
      <input id="submitUserModel" type="button" value="run on server">
  </div>
  </form>

function initializeUserModel(){
  let model = document.getElementById("modelArea").value;
  fetch('http://localhost:8080/', {
      method: 'post',
      headers: {'Content-Type': 'text/plain'},
      body: model
    })
      .then(response => response.json())
      .then(data => {
        console.log(data);
      }).then(console.log("received!"))     
}  

Answer 1

I got to the bottom of this. It turns out that the problem was due to VS Live Server which was detecting a change in the folder and hot-loading the app. The change was due to the backend, in the same folder, saving a log. Really silly thing to miss...

Answer 2

If you want to trigger your function when the form is submitted then you can use the "onsubmit" event listener available on HTML forms.

So you would do onsubmit="initializeUserModel(event)" . You pass it the event object so you can call event.preventDefault() in the function and stop the page from reloading.

Change your input to type="submit" (or make it a button of type="submit") or the form submission won't be triggered.

    <form id="modelCodeForm" onsubmit="initializeUserModel(event)">
      <label for="codehere"></label>
      <div id="modelAreaDiv">
        <textarea id="modelArea" cols="60" rows="20">Stuff</textarea>
        <br />
        <input id="submitUserModel" type="submit" value="run on server" />
      </div>
    </form>

  function initializeUserModel(event) {
    event.preventDefault();
    let model = document.getElementById("modelArea").value;
    fetch("http://localhost:8080/", {
      method: "post",
      headers: { "Content-Type": "text/plain" },
      body: model,
    })
      .then((response) => response.json())
      .then((data) => {
        console.log(data);
      })
      .then(console.log("received!"));
  }